thank you!
I had not gone there yet.
Primarily because “% moisture” seemed easier for the others involved in the transaction to wrap their head around.
given the variety of options out there, I’d still appreciate a leg up (product review 
) from anyone using a portable (or lab based) water activity meter to screen their incoming or out going biomass.
the pawkit (is that Australian for pocket?) seems portable enough.
Edit: $2600 is the first quote I got on this…,
$10k for the one @Dirteagle lists below.